Blood pumps are commonly used as elements of mechanical circulatory support devices or “MCSDs.” MCSDs are normally used to aid the pumping action of a diseased heart. An MCSD that is arranged to aid the pumping action of a ventricle is also referred to as a ventricular assist device or “VAD.”
A blood pump used in an MCSD typically is implanted within the patient, with the inlet of the pump communicating with a chamber of the heart, such as a ventricle and with the outlet of the pump connected to an artery. The pump is actuated to draw blood from the ventricle and pump it into the artery. The heart continues to beat, so that some blood may also be passed out of the ventricle through a valve such as the aortic valve. A condition referred to as a “suction” condition can occur when VAD tries to draw more blood than is available. When such a suction condition occurs, the chamber of the heart may collapse, so that a wall of the chamber is drawn toward the pump inlet and blocks the inlet. In extreme cases, such a condition can cause bruising or other injury to heart tissue. Moreover, the chamber wall may remain in place at the pump inlet for some time after the imbalance in flow has been corrected. Accordingly, MCSDs commonly incorporate control circuitry that maintains the flow through the pump at a safe value unlikely to cause a suction condition.